1. Field of the Invention
The present invention relates to a device for controlling a mechanical super charger in an internal combustion engine.
2. Description of the Related Art
Known in the related art, e.g., Japanese Unexamined Patent Publication (Kokai) No. 56-167817, is an internal combustion engine provided with an electromagnetic clutch between the supercharger and the engine crankshaft for controlling the supercharger. The clutch is selectively engaged or disengaged in accordance with the engine condition for the optional supercharging operation. For the highest fuel consumption efficiency, the clutch should be engaged at as high an engine speed as possible. However, too high an engine speed causes a shock upon clutch engagement and damage to the frictional surfaces of the clutch. Therefore, the engine speed for clutch engagement is kept low enough to balance the requirements of fuel consumption efficiency with the prevention of shock and clutch damage. In addition to the control based on the engine speed, the clutch is also controlled by the ratio of intake air amount to the engine speed. That is, the clutch is engaged when the ratio is large and is released when the ratio is small. In engine starting the engine the ratio can exceed the clutch engagement level irrespective of very low engine speed during the cranking, thus connecting the engine to the supercharger. This means the starter has to bear both the load for cranking the engine and the load for rotating the supercharger. As a result, it becomes difficult to start the engine.